SOWETO, South Africa -- When South African President Jacob Zuma walked into the stadium for the memorial service of Nelson Mandela, he drew a cheer from the ruling African National Congress crowd. But then little by little, the booing started.

In what should have been Zuma's finest hour, the people were jeering him.

And not at some unruly ANC conference. They chose one of the most momentous events in recent South African history, with more than 100 foreign dignitaries and the entire Mandela clan watching.

Oh my.

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One tweeter called the crowd “ungovernable.” Another asked, “Were they drunk?” Many criticized the actions of those who booed as an embarrassment to South Africa and a dishonor to Mandela.

Some sections of the crowd did cheer heartily for Zuma. His supporters, clad in ANC regalia, insisted that members of the crowd were simply chanting “Zu-ma, Zu-ma” in praise of the leader. But ANC spokesman Jackson Mthembu acknowledged and condemned the booing.

Local media reported that some in the crowd accompanied the jeers with a rolling gesture of both hands, used at ANC conferences to call for a leadership change.

Zuma was reelected as ANC leader last year, putting him in position to automatically gain the presidency after elections next year that the ANC is bound to win. But the reaction from some in Tuesday's crowd raises questions about his future, analysts said.

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The contrast with the adulation shown for President Obama was stark. When the image on a screen in the stadium switched from Obama and First Lady Michelle Obama to Zuma, people switched from clamorous exultation to jeering.

The man Zuma replaced as president, Thabo Mbeki, also received deafening cheers.

At one point, deputy president and master of ceremonies Cyril Ramaphosa, who appeared taken aback by the crowd's reaction, told them to be disciplined.

The booing died down when Zuma addressed the crowd in a stadium that seemed disappointingly empty. But in contrast to the spontaneous applause that burst forth throughout Obama’s speech, people chatted during much of Zuma’s address and those of other world leaders.

Some local media reported that the booing was coming from ANC supporters, while others said members of a radical opposition party were present.

The former Anglican archbishop of Cape Town, Desmond Tutu, later scolded the crowd for lack of discipline during a closing ceremony, demanding a pin-drop silence and getting it.  

A year ago, Zuma was riding high at the ANC national conference, when his ticket steamrollered the opposition.

But as the party heads into next year's elections, the ANC faces anger over unemployment and lack of services. It also has to deal with a challenge from the radical opposition party led by firebrand former ANC youth leader Julius Malema, which may draw votes from traditional ANC supporters.

The crowd’s performance Tuesday could also fuel a campaign by some in the ANC to put forward an alternative leader next year.

Many in the stadium were mortified.